1. Technical Field
The invention relates generally to the generation and manipulation of radiation, and more specifically to a method of managing radiation using a semiconducting device.
2. Related Art
Currently, neither electronic nor photonic devices generate radiation having a frequency within the terahertz range. As a result, this range of frequencies is often called the “terahertz gap.” For example, the upper frequency that can be attained using electronic transistors is limited by the transit time of carriers under the gate (for a field effect transistor) or across the base and collector depletion region (for a bipolar junction transistor). While the feature sizes of these devices can be scaled to obtain device parameters close to the terahertz gap (i.e., frequencies of a few hundred gigahertz), fundamental physics limitations, such as the size of the gate length versus the wave length of the terahertz radiation, lead to diminishing returns provided by further scaling. Photonic devices have been created that approach the terahertz gap using interband or intersubband transitions. However, these devices must operate at cryogenic temperatures due to the smaller quanta of terahertz radiation versus thermal energy at room and liquid nitrogen temperatures.
As an alternative approach, plasma waves have been used to generate radiation in the terahertz gap. Plasma waves are oscillations of electron density in time and space. The properties of plasma waves are dependent on the electron density and the dimension and geometry of the electronic system. In a gated two-dimensional electron gas, for example, the velocity of the plasma waves is proportional to the square root of the electron sheet density. In deep submicron field effect transistors, typical plasma waves have frequencies in the terahertz range and do not involve any quantum transitions. Further, the electron transit time may become smaller than the electron momentum relaxation time, causing the electron transport to approach a ballistic mode of transport.
Devices having a ballistic mode of transport exhibit two characteristics. In low electric fields, the effective electron mobility in short channel (i.e., submicron) devices may be substantially smaller than the electron mobility in long channel devices. In high electric fields, electron velocity is higher than in a collision dominated device, and the bulk plasma oscillations may lead to space oscillations of the electron density. When the plasma frequency multiplied by the electron momentum relaxation time is greater than one, a channel of a field effect transistor can act as a resonant cavity for the plasma waves. However, current devices have been unable to overcome the electron energy loss in a ballistic device due to the contacts of the device.
As a result, a need exists for a method of generating and manipulating radiation using a semiconducting device that allows for a larger gate length and/or successfully overcomes the electron energy loss due to the contacts of the device.